The femoral component of a hip joint endoprosthesis consists essentially of a shaft for anchoring in the core of the long bone or hollow bone of the thigh, and an approximately spherical-segment-like head for replacement of a diseased hip head, which is arranged or mounted on the proximal end of the anchoring shaft in such a manner so that it forms a load carrying unit with the anchoring shaft. While in such prostheses the anchoring shaft and the ball head frequently consist of the same type of material and are inseparably welded together with one another, in a different connection between the prosthesis head and the anchoring shaft a type of plug-connection is provided.
In this, a load-carrying tenon or peg in the form of a cone is arranged on the proximal end of the anchoring shaft, onto which in turn the prosthesis head is plugged or set. Such an arrangement has become known from the DE 2 921 529 A1. In this known arrangement, the connection between the head and the tenon or peg carrying it is releasably embodied, whereby it is possible, during the operation and depending on the indications, to use on the carrying tenon or peg either a head with larger diameter for the replacement of a diseased hip head and thereby to implant a so-called hemi-prosthesis, or instead a head of smaller diameter to supplement or complete this by means of a replacement socket to form a total hip endoprosthesis.
Such hip joint endoprostheses are only reliably utilizable if, in addition to a problem-free anchoring of the prosthesis shaft in the femur, the long time functions of the tenon or peg support that carries the head and of the head itself are also ensured. Thus, especially with conical insertion or plug-in connections typically utilized for prosthesis heads of oxide ceramic for producing a mechanically secure and slip-free clamping or jamming between the cone-shaped, generally metallic, supporting tenon or peg of the anchoring shaft and the metal or ceramic head, there arises the problem of the loosening of the originally mechanically secure connection as well as the disruption or destruction of the surface of the material pairing of head and shaft. Thereby however, corrosion processes can be triggered, which sometimes throw the integrity of the prosthesis completely into question. Moreover, an inadequate fitting of a ceramic head with the metallic tenon or peg can lead to increased stresses in the ceramic, with the result of a subsequent fracture of the implant component. Furthermore, the setting or plugging of a ceramic head onto a shaft left in-situ in the context of a replacement or exchange operation always represents a critical process.
For this reason, an already known measure is to provide a metal sleeve in a ceramic head of a hip joint endoprosthesis, which metal sleeve is joined on the one hand with the ball head and on the other hand with the tenon or peg. In the previously known arrangements, the joining of the sleeve with the ball head occurs either intra-operatively by the operating surgeon or it is already pre-operatively pressed into the ball head. In this regard, an arrangement is known from the U.S. 2006/0188845 A1, in which a metallic sleeve is selectively soldered or shrunken into a similarly metallic blind-hole-type inner recess of a ceramic head.
Moreover, from the DE 10 2012 014 345 A1, a femoral component of a hip joint endoprosthesis of the initially mentioned type has become known, in which the joining of the metallic sleeve with the blind-hole-type inner recess of a ceramic head is achieved pre-operatively in every case, wherein the connection or joint between the ceramic head and the sleeve is produced via a glass solder.